1. Field of the Invention
The present invention relates to a lens barrel in which a lens group is collapsed in one state and the lens group extends out toward a predetermined position in another state.
2. Description of the Related Art
In an imaging apparatus such as a digital camera or a digital video camera (hereinafter, referred to as a digital camera), improvement in photographic performance and a portability has been highly required. Therefore, the imaging apparatus has a lens barrel in which a photographic lens having a plurality of lens groups is built in, so as to allow focal length to be variable. In the imaging apparatus, at least one lens group is retracted from the photographic optical axis while the lens groups are collapsed and stored in a camera housing with minimum distances from each other less than distances required for photographing in a non-photographic state and the lens groups extends out from the camera housing so as to have distances from each other sufficiently for photographing in a photographic state. In such an imaging apparatus, the focal length is changed to perform photographing with a desired field of angle and the lens barrel is set in a collapsed state to be preferable for portability.
However, in this technology, the stored position of the lens group retracted from the photographic optical axis is substantially inner side of the maximum diameter of the fixed cylinder of the camera body. Therefore, although the size in the photographic optical axis direction in a state where the movable cylinder is stored in the camera body can be reduced, the outer diameter of the fixed cylinder increases so that the camera body becomes large when being viewed from a front (object) side.
Then, it has been known that at least one lens group is retracted out of the inner diameter of the movable cylinder by a retractable lens retaining frame (see Japanese Patent Application Publication No. 2006-330657). In this lens barrel, the retractable lens retaining frame is retracted out of the movable cylinder by a driving force from a driving mechanism in the collapsed state (when not photographing). The driving mechanism has a main guide shaft parallel to the photographic optical axis, a compression torsion spring provided on the main guide shaft, a lead screw parallel with the main guide shaft, and a female screw member screwed with the lead screw via a screw hole. The retractable lens retaining frame is supported movably along a longitudinal direction of the main guide shaft and rotatably about the main guide shaft. By the compression torsion spring supported by the main guide shaft, a rotation biasing force for biasing the lens retaining frame onto the photographic optical axis about the main guide shaft as a base point, a linear biasing force on the main guide shaft in the collapsed direction are applied to the retractable lens retaining frame. The female screw member moved along the axis of the lead screw by the rotation of the lead screw is connected to the retractable lens retaining frame via the cam structure. The cam structure is configured to convert the movement of the female screw member on the axis into a rotary motion of the retractable lens retaining frame about the main guide shaft against biasing of the compression torsion spring and a linear motion of the retractable lens retaining frame along the main guide shaft against biasing of the compression torsion spring. In this lens barrel, the lead screw is appropriately driven to be rotated to move the female screw member and thereby the retractable lens retaining frame is rotated about the main guide shaft against the rotation biasing force so as to retract the retained lens group out of the inner diameter of the movable cylinder. Thereby, in the lens barrel, compared with the conventional configuration in that the lens group is retracted inside the fixed cylinder, the outer diameter of the movable cylinder can be prevented from increasing without increasing distances between lens groups in the collapsed state.
However, in the conventional lens barrel, the lead screw is screwed with the female screw member with the screw hole in which the lead screw is inserted, the female screw member is rotated with the rotation of the lead screw so that there is possibility that the connection between the female screw member and the retractable lens retaining frame in the cam structure is released. In order to prevent this rotation, the female screw member has a rotation stop projected portion and the rotation stop projected portion is inserted in a guide groove extending along the axis line of the lead screw. The rotation stop projected portion is loosely fitted in the guide groove so as to allow the female screw member to be smoothly moved. Therefore, in the driving mechanism, one side surface of the rotation stop projected portion in accordance with the rotational direction of the lead screw comes into contact with one side surface of the guide groove and when the lead screw is inversely rotated, the rotation stop projected portion is rotated in the guide groove and the other side surface of the rotation stop projected portion comes into contact with the other side surface of the guide groove. Therefore, in the conventional lens barrel, due to the loosely fitting of the rotation stop projected portion and the guide groove, when the lead screw is inversely rotated, it is possible that hitting sound of the rotation stop projected portion onto the guide groove is generated and the position of the female screw member on the lead screw, that is, the position of the retractable lens retaining frame in the photographic optical axis direction differs in difference of the rotational direction of the lead screw.